For illumination purposes high CRI light sources are generally preferred. White LEDs based on a single YAG:Ce luminescent colour converter usually reach Ra values in the 70s with very bad colour rendering in the red spectral region. Therefore strong pressures exist for the development of efficient illumination grade white LEDs with excellent colour rendering over the entire visible spectral region. The obvious measure to improve colour rendering is the addition of a red emitting luminescent material (i.e. disclosed in the U.S. Pat. No. 6,717,353). However fabrication of white LEDs becomes more cumbersome due to the added degrees of freedom. Thus single phosphor options are deemed to be favourable if not superior.
However, there is still the continuing need for novel emitting luminescent materials which are usable within a wide range of applications and especially allow the fabrication of white phosphor converted LEDs (pcLEDs) with correlated colour temperature below 6000 K, optimized luminous efficiency and color rendering.